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The present invention relates generally to medical devices for joining tubular structures. More particularly, this invention relates to anastomosis staples composed of bioabsorbable and metallic components for connecting blood vessels.
An anastomosis is a surgical procedure by which two separate tubular bodies or ducts, usually blood vessels, are interconnected. The anastomotic connection allows body fluid to flow between the lumens of the tubular bodies without leakage at the connection site. Such a connection may be required to repair severed blood vessels. More often, anastomotic connections are utilized in order to bypass an obstruction in a patient""s heart. For example, in a coronary artery bypass graft (CABG) surgery, a graft vessel is anastomosed to the coronary artery downstream from the obstruction to enable aortic blood carried by the graft vessel to be rerouted around the blockage in the coronary artery. In one case, the anastomosis may be made between the end of the graft vessel and the side wall of the coronary artery, in what is typically known as an end-to-side connection. In other instances, the anastomotic connection could be of the side-to-side type. And in certain situations, more than one anastomotic connection may be needed.
Current methods available for creating an anastomotic connection include hand suturing the vessels together. However, the use of sutures to connect interrupted vessels has inherent drawbacks. For example, suturing is difficult to perform and time-consuming, and requires great skill and experience on the part of the surgeon due in large part to the extremely small scale of the vessels. Suturing is particularly difficult in beating heart CABG surgery. Also, sutures do not always provide a fluid-tight connection at the anastomosis site. Moreover, to perform the procedure it is usually necessary to stop the heart by infusing the organ with cold cardioplegia solution. This enables a blood-free and still anastomosis site for the suturing process. However, such procedures for slowing down or stopping the heart inherently result in trauma to the organ.
Attempts have been made to provide implantable devices that connect blood vessels together in a more expedient and reliable manner. One approach is to use staples to create an anastomotic connection. For example, Kaster et al. in U.S. Pat. No. 5,234,447 describes a staple comprising a rigid metal ring having fingers radially extending therefrom. Using a staple forming tool, the fingers are deformed to urge them into engagement with the vessels"" interior and exterior walls, thereby creating an anastomotic connection between the vessels.
One potential problem arising with staples having rigid annular members is compliance mismatch. The use of flexible metallic anastomotic staples for CABG procedures has recently been proposed to address this problem. Some of these flexible staples are described by Gifford, III et al. in U.S. Pat. Nos. 5,695,504 and 5,817,113, Backinski et al. in U.S. Pat. No. 6,036,702, and by Derowe et al. in WO 99/62408. These staples have flexible annular means that may reduce the rigidity of solid annular members of other staples such as the one described by Kaster et al.
In addition, use of flexible metallic stents has been contemplated to address the problem of compliance mismatch. Nevertheless, stents may eventually suffer from physiological phenomena such as intimal hyperplasia and stenosis. Gifford, III et al. in U.S. Pat. No. 5,695,504 attempts to overcome the problem of intimal hyperplasia by providing a non-absorbable flexible filament as a base to hold vessel engaging members. However, the non-absorbable flexible filament may not have the rigidity needed to deploy the staple, and may further radially constrain the vessel. Finally, the nonabsorbable filament may sterically hinder secondary interventional techniques such as balloon angioplasty that may become necessary at a future time.
Current designs for vascular anastomotic staples generally are more successful in large diameter proximal anastomoses. However, their utility in smaller diameter proximal anastomoses and distal anastomoses may be limited. Most of the anastomotic staples described in the art have rigid or substantially rigid annular members that serve as the base for vessel engaging members. These annular members may induce neointimal hyperplasia through a mechanism similar to that observed with metallic stents. Another potential problem with these annular members is that they may preclude the possibility of interventional means to address the hyperplasia, such as balloon angioplasty. Finally, rigid or semi-rigid metallic annular members may complicate the use of secondary interventional devices such as balloon or stent-carrying catheters by sterically preventing or hindering access to lesions distal to the staple.
There is thus a need for a vascular anastomosis staple that provides fast and reliable anastomosis in small diameter vessels. There is also a need for an anastomosis staple that prevents incurrence of neointimal hyperplasia. Finally, there is also a need for an anastomosis device that does not sterically hinder access to the surrounding tissue by other devices such as catheters.
The present invention avoids the aforementioned problems associated with anastomotic staples having rigid or semi-rigid annular base members by providing an anastomotic staple consisting of a plurality of vessel engaging members and a binding structure holding each of the plurality of vessel engaging members in a predefined spatial relationship. The binding structure includes at least one bioabsorbable element. As the anastomosis heals, the bioabsorbable element is resorbed, enabling at least one vessel engaging member to freely move with respect to at least one other vessel engaging member. Resorption of the bioabsorbable element relieves the anastomosis of its rigid constrainment imparted by the binding structure of the anastomosis staple.
In an exemplary embodiment, the composite staple of the present invention has a binding structure composed of a bioabsorbable polymeric or copolymeric scaffold. The scaffold is rigid enough to allow deployment of the device and quickly resorbs to avoid problems associated with intimal hyperplasia, compliance mismatch and physical hindrance of secondary interventional procedures. The scaffold may be either annular or elliptical in shape. In one aspect of this embodiment, the vessel engaging members are composed of superelastic or shape memory metal such as nitinol and are independent from one another, i.e., no metallic contacts are present from one member to the next. The members may be equidistant from one another and are embedded within the resorbable scaffold. Each vessel engaging member has a central body that is larger in diameter than the rest of the member. This central region facilitates anchorage within the bioabsorbable scaffold. In another aspect, the vessel engaging members are formed of a rigid but malleable metal such as stainless steel.
In yet another aspect of the present invention, the absorbable scaffold can act as a drug or radiation release vehicle. The scaffold may contain pharmaceutical agents and/or radioactive substances for the controlled release of such pharmaceutical agents and/or radiation after the composite staple is deployed. For example, the scaffold may contain antibiotics, anticoagulants, procoagulants, radioactive molecules with a short half-life and a xcex2-component, such as 131I. In addition, the vessel engaging members can be coated with a radioactive substance such as 32P to reduce the likelihood of neointimal hyperplasia. The members may also be coated with a non-radioactive ligand which can be rendered radioactive with subsequent intravenous administration of radioactive ligands.
In another embodiment of the present invention, the scaffold of the composite staple has an arcuate geometry suitable for anastomosing small diameter blood vessels. The scaffold may have an arc that matches the diameter of the target vessel to which the staple is connected, enabling the staple to saddle the vessel in conformity.
In yet another embodiment of the present invention, the composite staple has a binding structure comprising a radially expandable bioabsorbable scaffold and a plurality of vessel engaging members that are at least partially embedded within the scaffold. The scaffold comprises a plurality of alternating nodes and arched bands. Embedded within each node is a vessel engaging member having at least one arm extending out of the node. Between each node is an arched band that provides radial tension to the scaffold and enables the scaffold to radially expand.
In still another embodiment of the present invention, the composite staple includes a plurality of vessel engaging members and a plurality of bridges. Each pair of adjacent vessel engaging members is connected by at least one bridge. At least one pair of adjacent vessel engaging members is connected by a bioabsorbable element. The vessel engaging members and bridges are formed of the same material. Collectively, the bridges and bioabsorbable element make up the binding structure of the composite staple. The bridges provide for radial expansion of the composite staple. The binding structure of this particular composite staple may be considered a network of elements that hold the vessel engaging members in a predefined spatial relationship and imparts enough rigidity to deploy the composite staple. Upon resorption of the bioabsorbable element of the binding structure, the anastomosis is relieved of any constrainment, enabling at least one vessel engaging member to move freely with respect to another vessel engaging member.
Finally, in yet another embodiment of the present invention, the composite staple comprises a bioabsorbable scaffold having a plurality of vessel engaging members at least partially embedded within the scaffold. The scaffold may have an annular or elliptical shape. Each of the vessel engaging members has at least one protrusion that extends beyond the outer surface of the scaffold. The protrusions provide the composite staple with a roughened surface for effecting an anastomotic connection.
Further features of the invention, its nature and various advantages, will be more apparent from the accompanying drawings and the following detailed description of the drawings and the preferred embodiments.